The present invention relates to electrically conductive composites, and is particularly concerned with the provision of electrically conductive composites formed of a dielectric porous substance containing a conductive pyrrole polymer in the pores of the substance, and produced by electrochemically precipitating such pyrrole polymer from an electrolyte solution containing a pyrrole monomer and a non-nucleophilic anion, said porous substance being in contact with the anode, the resulting composite having good electrical conductivity and mechanical properties corresponding to those of the initial porous substance.
In the past several years, organic polymers have been discovered which have metallic properties, particularly electrical conductivity up to about 1000 ohm.sup.-1 cm.sup.-1. These polymers include doped polyacetylene and polypyrrole.
Although there are many potential applications for conducting polymers, their use has been limited by the fact they are chemically unstable, have poor mechanical properties and/or are difficult to produce in suitable forms.
Polypyrrole which is chemically more stable, for example, than the doped polyacetylene, has the disadvantage of being very brittle. Thin polypyrrole films from about 10 .mu.m to 20 mil thick have been produced on electrodes by electrochemical polymerization. However, these prior art films are too thin and too brittle to be useful in most structurally related applications. Particularly, the brittleness of such conducting polymer films renders their handling for large area applications extremely difficult, if not impossible.
Polypyrrole is produced by electropolymerization as described by A. F. Diaz, et al in an article entitled "Electrochemical Polymerization of Pyrrole" in the Journal of Chemical Society, Chemical Communications, 1979, page 635. N-substituted analogs of pyrrole such as N-methylpyrrole and N-phenylpyrrole have been used to form pyrrole polymers as reported by A. F. Diaz, et al in an article entitled "Electrochemistry of Conducting Polypyrrole Films" in the Journal of Electroanalytical Chemistry, 129, (1981) pages 115-132. The products produced in these processes are thin (from 20 .mu.m to 30 .mu.m) free-standing films in which anions from the electrolyte, such as tetrafluoborate and perchlorate, are used to dope the polymer and balance the cationic charge of the polymer backbone. However, the resultant polymer film is brittle and does not have the bulk and ductility needed to make the material useful in structural-related applications.
U.S. Pat. No. 4,401,545 to Naarmann, et al, discloses electrically conductive polypyrrole complexes with nitroaromatic anions as dopants, prepared by the anodic oxidation of a pyrrole in a polar solvent, in the presence of a salt of an acidic nitroaromatic compound. However, the thickness of the resulting electrochemically produced polypyrrole complexes is limited and the resulting films are also relatively brittle and hence also have limited structural applicability.
An object of the present invention is to provide a material comprising a conducting polypyrrole, having reduced brittleness and improved structural integrity.
Another object of the invention is to provide an electrically conductive composite formed of a substantially non-conductive or dielectric porous substance and a conductive polypyrrole.
A still further object of the invention is the provision of a process for imparting structural integrity to conductive polypyrrole by impregnating a dielectric porous substance with a pyrrole polymer.